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3A week 2 - lower GI tract > anatomy and physiology of large bowel > Flashcards

anatomy and physiology of large bowel Flashcards

1
Q

what are the 3 main functions of the colon

A
  1. finish absorption of nutrients + water
  2. synthesize certain vitamins (vit K etc.)
  3. form + eliminate faeces
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2
Q

what characteristic feature of the GI tract is absent in the colon

A

villi

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3
Q

where does the colon extend from

A

appendix to anus

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4
Q

why is small bowel obstruction more common than large bowel obstruction

A

small bowel is half the diameter of the large bowel

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5
Q

what is the caecum

A

a sac-like structure that is suspended inferior to the ielocaecal valve (R side) and it receives the contents of the ileum

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6
Q

what type of tissue is contained in the appendix and what does this suggest about its function

A

lymphoid tissue - suggest immunological function

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7
Q

what is the associations of UC and crohns with appendicectomy

A

reduced risk of UC but increased risk of crohns

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8
Q

what parts of the colon are retroperitoneal

A

ascending and descending colon

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9
Q

what parts of the colon does the mesocolon tether to the posterior abdo wall

A

transverse and sigmoid

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10
Q

what are taeniae coli

A

three bands of smooth muscle that make up the longitudinal muscle layer of the muscularis of the large intestine (apart from the terminal end)

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11
Q

what are the haustra

A

pouches formed by the contractions of taeniae coli causing the colon to bunch up

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12
Q

what are epiploic appendages

A

small fat-filled sacs of visceral peritoneum attached to the taeniae coli

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13
Q

where in the large bowel are taeniae coli and haustra not present

A

the rectum - here there are well developed layers of muscularis that create strong contractions required for defecation

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14
Q

at what vertebral level is the rectum

A

S3

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15
Q

what are the rectal valves + function

A

3 lateral bends that create a trio of internal transverse folds that support the weight of faecal matter and help to separate faeces from gas so that they are not passed simultaneously

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16
Q

where is the anal canal located

A

in the perineum, completely outside the abdominopelvic cavity

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17
Q

what is the internal anal sphincter muscle

A

a thickened extension of the circular SMOOTH muscle layer surrounding the colon -> contractions are involunatry

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18
Q

what is the external anal sphincter

A

a flat plane of SKELETAL muscle that is under voluntary control

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19
Q

what kind of cells connects the anal canal to the skin on the outside

A

stratified squamous epithelial mucosa - these cells can withstand the high levels of abrasion as faeces pass through

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20
Q

what are anal columns

A

longitudinal folds of the mucous membrane that each houses a grid of arteries and veins

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21
Q

what is an anal sinus

A

the depression between the anal columns -> secretes mucus that facilitates defecation

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22
Q

what is the dentate line (anus)

A

aka the pectinate line -> a horizontal, jagged band that runs circumferentially just below the level of the anal sinuses and represents the junction between the hind gut and external skin

23
Q

why is there a difference in sensation on either side of the dentate line (anus)

A

the mucosa above is faily insensitive as it is innervated by visceral sensory fibres;
the mucosa below is very sensitive as it is innervated by somatic sensory fibres

24
Q

differences between the walls of the large and small intestines (2)

A
  1. no villi or circular folds in large
  2. less enzyme secreting cells in large
25
Q

what cells is the mucosa of the colon primarily made up of (3)

A
  1. simple columnar epithelium
  2. enterocytes (absorptive)
  3. goblet cells
26
Q

what commonly (unconciously) ingested substance strips the muscous layer from the gut

A

detergent -> may contribute to the development of IBD

27
Q

what is the role of mucous in the colon (2)

A
  1. eases the movement of faeces
  2. protects the intestine from the effects of the acids and gases produced by enteric bacteria
28
Q

what do the enterocytes absorb in the colon (3)

A
  1. water
  2. salts
  3. vitamins produced by intestinal bacteria
29
Q

what do the normal colonic bacterial flora aid with (2)

A
  1. facilitate chemical digestion + absoprtion
  2. synthesize certain vitamins (vit B7 (biotin), vitamin K, vit B5 (Pantothenic acid))
30
Q

how are bacteria prevented from crossing the mucosal barrier in the gut

A
  1. peptidoglycan in the bacteria cell walls activate the release of chemicals by the epithelial cells which attract immune cells into the mucosa
  2. dendritic cells open the tight junctions between the epithelial cells and extend probes into the lume to evaluate the antigens
  3. APC dentritic cells travel to neighboring lymphoid tissue
  4. T cells detect the antigens and trigger an IgA mediated response
31
Q

how much liquid is resorbed in the small bowel a day

A

around 8L (of the 9L in the GI tract)

32
Q

what regulates the movement of chyme into the caecum

A

the ileocaecal sphincter

33
Q

what tiggeres colon movements (mechanical digestion)

A

distention of the caecum

34
Q

what is the action of fibre (2)

A
  1. softens stool
  2. increases the power of colonic contractions, optimising the activities of the colon
35
Q

what part of the colon d haustral contractions generally occur

A

the transverse and descending colon

36
Q

what type of movement is seen in haustral contractions

A

sluggish segmetation

37
Q

what causes chyme movement through the haustra

A

distension of a haustrum with chyme causes the muscle to contract and residue to be pushed into the next haustrum

38
Q

how frequently do haustral contractions occur

A

every 30min, each lasting 1 min

39
Q

3 components to mechanical digestion

A
  1. haustral contactions
  2. peristalsis
  3. mass movement
40
Q

what is mass movement (mechanical digestion)

A

strong waves starting midway through the transverse colon and quickly force the contents towards the rectum

41
Q

how frequently do mass movements occur (digestion)

A

3-4 times a day, either while eating or immediately after

42
Q

what is the gastrocolic reflex

A

distension of the stomach and the breakdown products in the small intestine trigger this reflex to increase motility -> mass movements

43
Q

what is responsible for chemical digestion in the large intesinte

A

solely bacteria -> no digestive enzymes are secreted

44
Q

what is saccharyoltic fermentation

A

when bacteria breakdown remaining carbs, discharging hydrogen, CO2 and CH4 gases that create flatusint he colon

45
Q

when is flatus production increased

A

when foods rich in otherwise indigestible (but the bacteria can digest them) surgars and complex carbs e.g. beans

46
Q

what is faeces formed up of (6)

A
  1. undigested food residues
  2. unabsorbed digested substances
  3. bacteria
  4. old epithelial cells
  5. inorganic salts
  6. water (to let it pass smoothly out of the body)
47
Q

how is the defecation reflex provoked

A

stretching of the rectal wall due to movement of faeces from the colon into the rectum (mass movement(

48
Q

what mediates the defecation reflex

A

this is a parasymp reflex mediated by the spinal chord

49
Q

what occurs in the defecation reflex (4)

A
  1. contraction of the colon and rectum
  2. relaxation of the internal sphincter
  3. initally - contraction of the external sphincter
  4. voluntary relaxation of the external sphincter
50
Q

describe the voluntary control of the defecation reflex

A

presence of faeces in the anal canal sends a signal to the brain indicating the need to deficate -> the external sphincter muscle can be voluntarily controlled so that defecation occurs at an appropriate time

51
Q

what will delayed defecation lead to (in terms of the stool)

A

increased water absorption leading to firmer stool -> potentially leading to constipation

52
Q

how does diarrhorea occur

A

waste material moves too quickly through the intestines and so not enough water can be absorbed -> can be a result of ingested pathogens

53
Q

what chart is used to describe stool

A

bristol stool chart

54
Q

how may types of stool are on the bristol stool chart

A

7 -> 1 is hard to pass and 7 is entirely liquid

3A week 2 - lower GI tract (8 decks)

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